Vertically adjustable or height adjustable patient supports, for example beds, are of great utility in hospital and extended care settings. Such beds are used in a lowered position to minimize the risk of injury to persons who may through inattention or infirmity fall out of the bed. The beds are used in an upper position to enable personnel to perform their functions with respect to the bed or its occupant without bending down or having to work in an awkward physical position.
Patient support decks of height adjustable beds may be raised or lowered by way of actuators, for example linear actuators. The actuators may be motor driven and may be attached to pivoting legs and a bed frame, while the legs are pivotally attached to the bed frame. When raising the patient support deck of such a bed from a lowermost position, one problem that arises is the greater motor power required to initiate the raising sequence action. Greater motor power at the lowermost position is required because the leg is tucked under the bed frame and virtually parallel thereto resulting in almost no effective angle between the leg and the bed frame.
One arrangement for overcoming this problem is disclosed in U.S. Pat. No. 7,185,377 issued Mar. 6, 2007. This arrangement comprises linear guide rods rigidly attached at both ends to the bed frame. Bearing blocks are rigidly connected to linear actuators and movably mounted on the linear guide rods. Spring members are mounted circumferentially on the linear guide rods. When the bed frame is in the lowermost position, the bearing blocks attached to the linear actuators longitudinally compress the springs between the bearing blocks and transverse cross-members of the bed frame. When the bed frame is sought to be raised the energy in the compressed springs act on the bearing blocks to assist the actuators during the first or initial movement along the linear guide rods. Once movement has been started and an effective angle established, the actuators alone are then capable of raising the bed frame the rest of the way.
Despite the improvements described in U.S. Pat. No. 7,185,377, there remains a need for more robust assemblies that assist motorized actuators in raising the patient support deck of a height adjustable bed from a lowermost position.